The present invention relates to a device for crimping or coupling end elements of a flexible pipe, the innermost element of which consists of a metal carcass, and to a method for implementing this device at the end of a flexible pipe.
A flexible pipe known as a rough bore generally comprises, as innermost elements, at least one internal metal carcass made of a spiral winding of a shaped filament such as a profiled and interlocked strip and a sealing sheath arranged over the metal carcass.
The present invention chooses to consider a flexible pipe whose metal carcass has discontinuities between the turns, the sealing sheath comprising, at each discontinuity, a crept part which at least partially fills the corresponding discontinuity.
These pipes often need to be coupled end to end with other pipes of the same diameter or of a different diameter or alternatively with another fixed structure, the couplings or joints being provided by an end fitting associated with the end of the pipe that is to be coupled.
The flexible pipe has to be fixed to each end fitting in such a way as to allow the continuity of the seal of the flexible pipe and the reaction of tensile loadings due to the bottom effect, which loadings are fully reacted by the tensile armor layers as is known.
Sealing between the end fitting and the sealing sheath is provided by means of a metal bushing with a roughly conical external surface, slipped and crimped onto the sealing sheath. The metal bushing also holds the sealing sheath axially in the connecting end fitting by opposing the residual axial stresses due to the specific method used to manufacture the flexible pipe. The sealing sheath is trapped between the metal bushing and the metal carcass, the latter having sufficient mechanical strength to withstand the crimping of the metal bushing.
The various elements involved in connecting between the end fitting and the end of the flexible pipe that is to be connected are described and depicted in FR-2 743 614 which is incorporated into the current application as regards those common parts which are needed for understanding the connection between an end of a flexible pipe and an end fitting.
That document also recommends the insertion of a tubular insert known as a hollow nipple between two layers consisting of a sacrificial sublayer in contact with the internal metal carcass and a sealing barrier, the sacrificial sublayer being intended to prevent the sealing barrier from creeping into the discontinuities between the turns of the metal carcass. The hollow nipple as described in that document has a tubular cylindrical central part and a rear end which tapers to a bevel, delimited on the outside by a conical surface with a vertex angle of between 3 and 30xc2x0. At the front end the hollow nipple has a shoulder, said shoulder defining an end stop for the sealing barrier. Furthermore, the hollow nipple is axially in abutment against a retaining ring secured to the front end of the internal metal carcass, said retaining ring in turn being secured to the end fitting.
Whatever the embodiment described in FR-2 743 614, the sealing barrier is not crimped directly onto the internal metal carcass but is crimped via a sacrificial layer arranged around said metal carcass. As a result, crimping is plastic to plastic, even in the case of the hollow nipple because the latter is inserted between the sealing barrier and the sacrificial layer.
WO 97/01 058 proposes a sealing system consisting of a sleeve which is inserted between the internal metal carcass and the barrier layers arranged adjacent to said metal carcass. The sleeve is cylindrical over practically its entire length and comprises a toothing on its external face adjacent to the lower barrier layer so as to hold said lower layer firmly and prevent it from slipping. In another embodiment, the sleeve has an end which is toothed in the manner of a saw and which cuts the lower barrier layer after insertion and rotation. A metal ring or bush crimps the barrier layers onto the cylindrical sleeve. The cylindrical sleeve also comprises a snap connector at one of its ends to secure the sleeve to the body of the end fitting.
These sealing devices or systems are ill suited to flexible pipes comprising a sealing sheath or barrier which has crept into the discontinuities between the turns of the internal metal carcass. This is because forcibly inserting the cylindrical sleeves or hollow nipples of the prior art somewhat damage the sealing barrier or sheath at the bulges or crept zones. Now, the even partial destruction of these crept zones may give rise to loss of sealing between the flexible pipe and the end fitting, for example following the creation of cracks in the sealing sheath. What is more, the forcible introduction of the hollow nipple or of the sleeve between the sealing sheath and the metal carcass causes lumps to form on the exterior surface of said sheath, in the region of the creep bulges or crept zones. The formation of these lumps if the creep bulges are not cut off is a drawback because either the clamping bush slipped onto the internal sleeve will not fulfil its role entirely because it needs to have an inside diameter at least equal to the outside diameter of the sheath in the region of said lumps in order easily to be slipped around the sheath, or the inside diameter is smaller than the outside diameter at the lumps and therefore the bush is not easy to slip on unless the creep bulges are cut off to obtain a roughly cylindrical external sheath surface in the region of the hollow nipple.
Other systems are described in U.S. Pat. No. 4,950,001, CA 734 830, U.S. Pat. Nos. 4,773,452 and 2,394,632. Such systems have a certain number of drawbacks and, in particular, they dictate tricky fitting of multi-part connection elements which do not naturally fit the end of the tube. These solutions entail not only inserting a coupling device within the constituent layers of the flexible pipe, but also screwing a nut on, sometimes with the addition of elements for reinforcing the pipe/coupling device connection, such as a curable powder or resin. In some instances, fitting the coupling device onto the end of the pipe is even irreversible or alternatively damages the constituent layers at the end of the pipe.
GB 586 488 discloses a system comprising a neck which is inserted between the metallic carcass and the sealing sheath. Nevertheless, the sealing sheath is on a smooth surface of the neck which creates bases at the locations of the creep areas.
The object of the present invention is to overcome the aforementioned drawbacks and to provide a simple crimping or coupling device which readily fits the end of a flexible pipe while at the same time maintaining the integrity of the internal sealing sheath.
The subject of the present invention is a device for crimping or coupling end elements of a flexible pipe which comprises a cylindro-frustoconical hollow nipple tapered at one end, part of said hollow nipple being inserted through the tapered end between the sealing sheath and the metal carcass, and which is characterized in that the hollow nipple has, over at least a portion of the inserted part, grooves which roughly correspond, in terms of shape, with the crept parts of the sealing sheath, so that once the hollow nipple has been introduced, at least some of said crept parts are almost entirely housed in the grooves of the hollow nipple.
Thus, the sealing sheath is not damaged at the bulges or creep zones in the discontinuities between the turns of the carcass and the external surface of the sheath in the region of the hollow nipple is practically cylindrical, which makes it easier for the clamping bush to be slipped onto said internal sheath.
According to another feature, the profile of the grooves of the hollow nipple is of trapezoidal shape open on the face that receives the crept parts of the sealing sheath. This opening of the groove makes it even easier for the crept parts of the hollow nipple to be introduced into said grooves as it gradually penetrates between the internal sealing sheath and the metal carcass.
According to another feature, the free edges of the grooves of the hollow nipple are rounded. As the hollow nipple is introduced between the sheath and the carcass, the crept parts of the sheath are then advantageously guarded against any damage by being chopped off or torn off by grooves which might otherwise be sharp-edged. The risk of damage to the crept parts of the sheath by the free edges of the grooves is also lower once the hollow nipple has been fully introduced.
According to another feature, the depth of the grooves of the hollow nipple is at least equal to the height of the crept part of the sealing sheath. The grooves thus have sufficient depth for the crept part of the sheath to be able to enter them easily over its entire height without possibly being compressed.
According to another feature, the angular aperture of the profile of the grooves of the hollow nipple is about 90xc2x0. This angular aperture is wide enough for the crept parts of the sheath to easily enter the grooves of the hollow nipple.
According to another feature, the vertex angle of the tapered end of the hollow nipple is between 5 and 30xc2x0. A small vertex angle also makes the hollow nipple easier to introduce into the flexible pipe, making insertion, to some extent, gradual.
Another subject of the present invention is a method for introducing the device into the end of a flexible pipe, said method being characterized in that it consists in heating the sealing sheath so as to soften at least the crept parts over the entire slip-on length of the hollow nipple, and in introducing the hollow nipple while said sheath is softened.
According to another feature, the system for heating the sheath consists of a chamber containing a certain volume surrounding part of the sheath at least in the region of the introduction zone, hot air being introduced into said volume to heat said part of the sheath. This simple device is easy to fit and allows the sheath to be heated uniformly at the introduction zone.
The invention will be better understood with the aid of the description which follows, with reference to the appended diagrammatic drawings depicting, by way of example, one embodiment of a device for crimping or coupling end elements of a flexible pipe. Other advantages and features will come to light upon reading the description.